The Python core team is experimenting with distributed version control. Python 2.5, 2.6 and 3.0 branches are now available under Bazaar. The Bazaar master is synced periodically from Subversion and may be slightly behind.
After the initial announcement there was some debate about which VCS to use. It was made clear that this is an experiment. No decision has been made about switching away from Subversion. This is more about experimenting with the distributed workflow. If it turns out that distributed VCS is the way to go then there would be open discussion about which system to use.
There is also an unofficial Mercurial repository. Antoine Pitrou set it up as an alternative to Bazaar. For more information read the announcement on the dev-python thread.